Extremely sensitive low cost sensors such as acoustic sensors are required for a wide range of applications, many of which involve operation under hostile environments. Typical examples include geophones or hydrophones used to record the response of the earth to acoustic impulses applied thereto in search for minerals and petroleum both on land and under water. It has been recognized that fiber optics may allow the construction of rugged high performance acoustic sensors. In particular, approaches have been developed successfully which are based on the comparison of light passed through a reference optical fiber shielded from acoustic noise with light passed through a second signal fiber which is subjected to the energy wished to be detected. One such approach is reported in U.S. Pat. No. 4,297,887 entitled "High-Sensitivity, Low-Noise, Remote Optical Fiber" by J. A. Bucaro. Unfortunately, such devices are not always able to provide features and desirable attributes such as automatic noise suppression, low cost, small size, simple design, and ease of incorporation in acoustic sensor arrays. These and other sensitive devices, such as taught by Cahill and Udd in U.S. Pat. No. 4,375,680, require electronic feedback mechanisms for readout and signal stabilization.